Deque on doubly linked list

Deque.java

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Created with IntelliJ IDEA.
 * User: Vitaly Stakhov
 * Date: 28/09/2012
 * Time: 16:49
 * To change this template use File | Settings | File Templates.
 */
public class Deque<Item> implements Iterable<Item> {

    private int size;
    private Node first;
    private Node last;

    public Deque() {

    }

    public boolean isEmpty() {
        return first == null;
    }

    public int size() {
        return size;
    }

    public void addFirst(Item item) {
        throwIfNull(item);

        Node newFirst = new Node();
        newFirst.item = item;

        if (first != null) {
            newFirst.next = first;
            first.previous = newFirst;
        }
        first = newFirst;
        if (last == null) last = first;

        size++;
    }

    public Item removeFirst() {
        throwIfEmpty();

        Node oldFirst = first;
        first = first.next;

        if (first == null)
            last = null;
        else
            first.previous = null;

        size--;

        return oldFirst.item;
    }

    public void addLast(Item item) {
        throwIfNull(item);

        Node newLast = new Node();
        newLast.item = item;

        if (last != null) {
            newLast.previous = last;
            last.next = newLast;
        }
        last = newLast;
        if (first == null) first = last;

        size++;
    }

    public Item removeLast() {
        throwIfEmpty();

        Node oldLast = last;
        last = oldLast.previous;

        if (last == null)
            first = null;
        else
            last.next = null;

        size--;

        return oldLast.item;
    }

    private void throwIfEmpty() {
        if (first == null)
            throw new NoSuchElementException();
    }

    private void throwIfNull(Item item) {
        if (item == null)
            throw new NullPointerException();
    }

    @Override
    public Iterator<Item> iterator() {
        return new ItemsIterator();
    }

    private class ItemsIterator implements Iterator<Item> {

        private Node current;

        public ItemsIterator() {
            current = first;
        }

        @Override
        public boolean hasNext() {
            return current != null;
        }

        @Override
        public Item next() {
            if (current == null)
                throw new NoSuchElementException();

            Item item = current.item;
            current = current.next;
            return item;
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException();
        }
    }

    private class Node {
        Item item;
        Node next;
        Node previous;
    }

}